1. Field of the Invention
The present invention relates to radio frequency (RF) channel management and in particular to channel management in which both 20 MHz and 40 MHz packets may be sent.
2. Related Art
Radio systems use frequency division to ensure that different RF devices can function in different frequency ranges. In this manner, for example, a user's cell phone does not interfere with a government's satellite. These frequency ranges are called bands.
According to the IEEE 802.11 family of standards, which governs wireless communications, the 2.4 GHz frequency band includes 14 frequency channels. FIG. 1A illustrates these 14 channels, wherein each channel when occupied has a 22 MHz bandwidth and is centered on a predetermined frequency, i.e. the center frequency labeled in FIG. 1A (note that a channel does not have an exact edge and thus may spread beyond the edges of its shown boundaries). In this frequency band, the center frequencies of adjacent channels are 5 MHz apart. Note that channels 12-14 are not used in the United States (in FIG. 1A, the usable channels in the U.S. are indicated by solid contour lines). FIG. 1B illustrates the 12 channels (i.e. channels 34, 36, 38, 40, 42, 44, 46, 48, 52, 56, 60, and 64) provided in the 5 GHz band. In this frequency band, each channel is 20 MHz wide, and the center frequencies of adjacent channels in the U.S. (which are indicated by solid contour lines) are 20 MHz apart.
Notably, using a wider channel could advantageously increase capacity, i.e. the transfer rate. For example, FIG. 2 illustrates a graph 200 that indicates theoretical capacity limits can be directly increased when effecting increases in bandwidth. Specifically, a 40 MHz channel (indicated by a curve 202) always has greater capacity than a 20 MHz channel (indicated by a curve 201), and increasingly so as the signal to noise ratio (SNR) increases. Unfortunately, 40 MHz channels are not currently permitted in some regions, such as Japan and Europe. Additionally, legacy devices in other countries, e.g. the United States, also rely on 20 MHz channels.
Therefore, a need arises to effectively provide 40 MHz communication using 20 MHz channels. A further need arises to efficiently provide and manage this 40 MHz communication.